The present invention relates to electroplating technology. In particular, the present invention relates to apparatus for electroplating, and more particularly, for electroplating of semiconductor wafers.
Deposition of metallic layers on semi-conductor wafers can be performed by electroless plating or electrolytic plating. In electrolytic plating, a wafer with a metallic seed layer is protected by a layer of photoresist, which in turn is etched by conventional photolithography to expose the prescribed pattern. Electroplating is then performed to deposit the selected metal or alloy on the pattern before the photoresist layer is removed. For flip chip production, an electroplating step is performed to produce the metallic input/output (I/O) pads that are required for electrical contact with external components. Solder bumps or stud bumps are then annealed or bonded onto the pads to form interconnections with the substrate.
The electroplating process typically involves the surface preparation, plating, rinsing and drying steps. Some of these steps require the use of corrosive chemicals that have to be carefully handled and contained. Therefore, it would be ideal to have the entire process confined within the same chamber. Furthermore, gas bubbles generated during electroplating tend to float upwards to adhere themselves to any object that is positioned near the top of the electrolyte solution. Thus, a system that allows the wafer to be positioned at the bottom of the electrolytic chamber is desired. In addition, rinsing and drying are often required for both the top and the bottom surfaces of the wafer, since the surface preparation fluid and electrolyte typically contaminate both surfaces. It is therefore an object of the present invention to provide a device that alleviates the aforementioned difficulties in electroplating.
Accordingly, the present invention provides, in one aspect, an electroplating chamber that allows flat-bottomed substrates, particularly disc-shaped substrates such as wafers to be effectively plated with the plating surface facing upwards. In another aspect, the substrate may be rotated to provided even plating. Rinsing and spin-drying may also be optionally applied such that the plating process assumes a convenient dry-in, dry-out process. In a further aspect, a method of reducing non-uniformity in the production process is provided using the apparatus according to the present invention.
The apparatus, constructed in accordance with the preferred embodiment, includes a chamber with a cover. The chamber is provided with a bottom having sidewall and an opening on top to allow access of the substrate to be plated. The bottom is provided with securing means for securing substrates into the chamber during the plating process and a barrier element adapted to contact the bottom edge of the substrate for preventing the electrolyte solution from flowing towards the bottom center of the substrate. Drainage means is provided in the chamber for draining liquids. At least one electrode retaining element having at least one first electrode extending therefrom. The electrode retaining element is movable between an operating position and a release position. The retaining element in the operating position is coupled to the bottom such that the first electrode is in contact with the substrate to be plated and is also electrically coupled to a power source. The retaining element in the release position is decoupled from the bottom to facilitate removal of the substrate.
The chamber can be closed by a chamber cover, which contains a supply mechanism for providing medium such as electrolyte or rinsing fluid into the chamber. The cover also contains a second electrode held above the substrate by an electrode holder. The electrode holder retains the second electrode juxtapose the substrate and defining a space therebetween wherethrough electrolyte solution flows during operation to complete the electrical connection. The two electrodes are connected to a DC power source during operation.
In the specific preferred embodiment, the electrode holder is a single-piece, ringed structure that can be coupled to a recess in the cover in the release position, such that lifting the cover will automatically move the ring away from the container. A series of vacuum outlets is provided at the sidewall of the chamber to secure the retaining element into the operating position. The bottom is preferably a rotatable chuck that allows processing while stationary, or during high speed or low speed spinning. This feature allows three steps of the electroplating process (i.e. plating, rinsing and drying steps) to be performed in the same chamber.
Using the apparatus according to the present invention, it is feasible and cost effective to have a sequential series of plating of a single substrate performed on different plating chambers. The method includes plating a fraction of the desired metallic layer in a first plating chamber, rinsing and drying the substrate with the partially plating surface; moving the partially plated substrate to a second chamber, and repeating the partial plating and rinsing/drying steps. Using this method, the non-uniformity in each chamber is evened out such that the resulting substrate contains an even and uniform plating layer.